Where Do Scary Diseases Like SARS and MERS Come From? Animals

Middle-Eastern Respiratory Syndrome, or MERS, has a lot in common with other emerging disease threats: we probably got it from animals.

MERS has sickened at least 500 people, including two who traveled to the U.S, and has caused 145 deaths. It's caused by a kind of coronavirus, a family of diseases that also include a microbe that causes Sudden Acute Respiratory Syndrome, or SARS. According to the Centers for Disease Control and Prevention, the viruses that cause both sicknesses are closest to coronaviruses seen in bats; camels can also infect humans. That means they're both likely to be zoonotic diseases, which is the science name for diseases that can be passed between animals and humans. Other major zoonotic diseases include anthrax, influenza, Lyme disease, malaria, Ebola and West Nile. According to the World Health Organization, that's just the tip of the iceberg: more than 200 diseases are zoonotic.

MERS-CoV (Photo credit: NIAID)

Zoonotic diseases account for about 75 percent of recently-emerging infectious disease threats, according to the CDC, and more than half of all human pathogens were acquired from animals. Any infection acquired from an animal can be termed "zoonotic;" once the virus appears to attempt making the jump permanent, it can be called an "emerging infectious disease."

The most recent zoonotic disease that you may have caught was the 2009 H1N1 swine flu. It bore no resemblance to the strains circulating at the time in humans; instead, it came from the guts of pigs, where influenza viruses can reassemble. It's not clear how often pathogens trying to jump to humans fail -- in fact, we've only recently developed the technology to track the spread of disease from animals to humans at all.

MERS is one of several emerging infectious diseases that appear to be trying to become human viruses. At first, there were animal contacts for the cases. Now it seems to be jumping between people. It's not entirely clear that the changes in the virus will make humans more susceptible. Perhaps we are seeing a random fluctuation in the number of people who are infected; perhaps we're just seeing more cases because we're watching more closely.

However, we have been seeing more symptomatic cases and larger clusters than before. More health care workers are becoming ill, and a greater proportion of the cases are in healthcare workers -- including both U.S. cases. Most cases until recently were zoonotic -- that is, in the sense that they were acquired directly from animals. But clusters involving 12-48 people are now springing up, with a single person infecting as many as 12. That change may also be due to better surveillance, but I doubt it.

That means we probably should start preparing for the virus to begin spreading more rapidly. The patient who was treated in Florida came into contact with 500 people while flying and the CDC is currently trying to track them all down. It was on the trip between Jeddah, Saudi Arabia, and London that this person first began to feel sick. But because it's not clear how or when MERS is transmitted, those people may be fine. MERS usually isn't dormant for longer than 14 days, so we will hear about any additional infections soon, if there are any to hear about.

Of course MERS may not go global; it may remain isolated. But instead of waiting to find out, it may be prudent to step up disease surveillance and begin to think about treatments. Antibodies to the respiratory syndrome have already been found, so with some work, we could develop a treatment -- or, better, a vaccine.

However, if we're concerned not just with MERS but with "the next MERS," whatever that may be, it behooves us to begin looking very closely at the animals in our environment. We know where many of these emerging diseases come from -- and now it's time to pay attention before they jump to humans. Maybe next time we'll be better-prepared.

I write about science, literature, and big ideas. Previously, I spent 7 years at Bloomberg, and my work has appeared in outlets including the Kenyon Review, Seed Magazine, the New York Observer, the Philadelphia Inquirer, the Awl, and Greenfriar. You can subscribe to my new...